Projection systems and methods

ABSTRACT

Image display apparatus and methods may use a single imaging element such as a digital mirror device (DMD) to spatially modulate plural color channels. A color channel may include a light steering element such as a phase modulator. Steered light from a light steering element may be combined with or replaced by additional light to better display bright images. These technologies may be provided together or applied individually.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.16/799,518 filed 24 Feb. 2020, which is a continuation of U.S.application Ser. No. 16/107,860 filed 21 Aug. 2018 now issued as U.S.Pat. No. 10,602,100, which is a continuation of U.S. application Ser.No. 15/724,141 filed 3 Oct. 2017 now issued as U.S. Pat. No. 10,469,808,which is a continuation of U.S. application Ser. No. 15/287,390 filed 6Oct. 2016 now issued as U.S. Pat. No. 9,848,176, which claims thebenefit under 35 U.S.C. § 119 of U.S. Application No. 62/237989 filed 6Oct. 2015 and entitled PROJECTION SYSTEMS AND METHODS, all of which arehereby incorporated herein by reference for all purposes.

TECHNICAL FIELD

One aspect of this invention relates to the generation of desiredpatterns of light in field sequential projection systems. Another aspectof this invention relates to the generation of desired patterns of lightin a projection system with multiple stages of image forming elements.These aspects may be applied individually or in combination. Embodimentsof the invention provide projectors, components for projectors, andrelated methods.

SUMMARY

This invention has a number of aspects. These may be practicedindividually or in various combinations. These aspects include withoutlimitation:

-   -   Image projection apparatus;    -   Image projection methods;    -   Apparatus and methods for mixing light that has been steered        onto an imaging element by a phase modulator with additional        light.

An example aspect of the invention provides a method for projecting acolor image. The method comprises for each of a sequence of fields, eachof the fields associated with a corresponding color, setting an imagingelement to spatially modulate light according to a pattern correspondingto the color and illuminating the imaging element with light of thecorresponding color. Illuminating the imaging element with light of thecorresponding color comprises directing light of the corresponding coloronto a phase modulator that is controlled to provide a phase patternoperative to steer the light of the corresponding color to desiredlocations on the imaging element. The phase modulator is refreshed at afrequency that is less than a frequency with which the fields of theseries of fields are presented. In some embodiments the phase modulatoris refreshed once per frame (where a frame comprises one complete cycleof fields of different colors).

In some embodiments a separate phase modulator is provided for each ofthe plurality of colors and the method comprises refreshing the one ofthe phase modulators corresponding to one of the plurality of colorsduring a field corresponding to a different one of the plurality ofcolors.

In some embodiments a distinct area of the phase modulator is associatedwith each one of the plurality of colors and illuminating the imagingelement with light of the corresponding color comprises directing lightof the corresponding color to illuminate the area of the phase modulatorassociated with the corresponding color while the area of the phasemodulator associated with the corresponding color is being controlled toprovide the phase pattern operative to steer the light of thecorresponding color to desired locations on the imaging element. In someembodiments the method comprises refreshing one of the areas of thephase modulator corresponding to one of the plurality of colors during afield corresponding to a different one of the plurality of colors.

The areas may have different sizes. For example, the plurality of colorsmay include blue and the one of the areas associated with blue may belarger than at least one other one of the areas; or the plurality ofcolors may include green and the one of the areas associated with greenmay be larger than at least one other one of the areas; or relativesizes of the areas may be controlled based on relative power levels forcolors of the plurality of colors in an image being displayed. In someembodiments the method comprises periodically reassigning some or all ofthe plurality of colors to different ones of the plurality of areas ofthe phase modulator. For example, the sequence of fields may repeat oncein each of a sequence of frames and the method may comprise reassigningsome or all of the plurality of colors to different ones of theplurality of areas of the phase modulator in each of the frames.

In some embodiments the same phase pattern is used for each of theplurality of colors.

In some embodiments the plurality of colors comprise red green and blue.

In some embodiments the imaging element comprises a DMD.

In some embodiments the phase modulator comprises an LCOS.

In some embodiments illuminating the imaging element with light of thecorresponding color further comprises combining additional light of thecorresponding color with the light that has been steered by the phasemodulator or replacing the light that has been steered by the phasemodulator with light that has bypassed the phase modulator. Combiningthe additional light with the light that has been steered by the phasemodulator may produce a beam of light that illuminates the imagingelement from a common direction. In some embodiments the additionallight comprises light collected from a DC spot produced by the phasemodulator. In some embodiments the additional light comprises light froman additional light source. In some embodiments the light that has beensteered by the phase modulator has a first polarization, the additionallight has a second polarization different from the first polarizationand the light that has been steered by the phase modulator is combinedwith the additional light at a polarizing beam splitter. In someembodiments the light that has been steered by the phase modulator has afirst wavelength, the additional light has a second wavelength differentfrom the first wavelength and the light that has been steered by thephase modulator is combined with the additional light at a dichroicelement. In some embodiments the light source emits light havingcomponents of two polarization states and the method comprisesseparating the components of the emitted light wherein the additionallight comprises one of the components of the emitted light and the lightthat has been steered by the phase modulator is made up of the other oneof the components of the emitted light. In some such embodiments themethod comprises altering the relative intensities of the components ofthe two polarization states by passing the emitted light through apolarization shifting element and controlling the polarization shiftingelement to vary a proportion of the light in each of the separatedcomponents based on a brightness of an image being projected.

Another example aspect provides a method for projecting a color imagethat comprises illuminating an imaging element with light of a color byselectively, based on a brightness or power level of the image:operating in a first mode wherein light of the color is directed onto aphase modulator that is controlled to provide a phase pattern operativeto steer the light of the color to desired locations on the imagingelement and: operating in a second mode wherein either: light of thecolor is either directed onto the imaging element from a light sourcewithout interacting with the phase modulator; or light of the color isdirected onto a phase modulator that is controlled to provide a phasepattern operative to steer the light of the color to desired locationson the imaging element and combined with additional light of the colorand the combined light is directed onto the imaging element.

Another example aspect provides apparatus for projecting images that isconfigured to implement any of the methods described herein.

Additional aspects of the invention and example embodiments of theinvention are illustrated in the drawings and/or described in thefollowing description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate non-limiting example embodiments ofthe invention. These drawings illustrate example projectors and alsoillustrate example methods.

FIGS. 1 through 9 relate to methods and apparatus which display imagesin a field sequential manner. Field sequential projectors employingsecondary colours or white as fields can also be represented using thesediagrams by turning on more than one light source at a time andadjusting the amplitude image on the Digital Micromirror Device (“DMD”).

FIG. 1 is a schematic illustration showing the red light path through aprojector operating according to a first approach where only the redchannel phase Liquid Crystal on Silicon (“LCOS”) is illuminated and theDMD only directs the red pixels to the screen.

FIG. 2 is a schematic illustration showing the green light path througha projector operating according to the first approach where only thegreen channel phase LCOS is illuminated and the DMD only directs thegreen pixels to the screen.

FIG. 3 is a schematic illustration showing the blue light path through aprojector operating according to the first approach where only the bluechannel phase LCOS is illuminated and the DMD only directs the bluepixels to the screen.

FIG. 4 is a schematic illustration showing the red light path through aprojector operating according to a second approach where only the redspatial portion of the phase LCOS is illuminated and the DMD onlydirects the red pixels to the screen. The single LCOS also displays thegreen and blue phase patterns in different locations but these are notilluminated in FIG. 4.

FIG. 5 is a schematic illustration showing the green light path througha projector operating according to the second approach where only thegreen spatial portion of the phase LCOS is illuminated and the DMD onlydirects the green pixels to the screen. The single LCOS also displaysthe red and blue phase patterns in different locations but these are notilluminated in FIG. 5.

FIG. 6 is a schematic illustration showing the blue light path through aprojector operating according to the second approach where only the bluespatial portion of the phase LCOS is illuminated and the DMD onlydirects the blue pixels to the screen. The single LCOS also displays thered and green phase patterns in different locations but they are notilluminated in FIG. 6.

FIG. 7 is a schematic illustration showing the red light path through aprojector operating according to a third approach where a luminancephase pattern on the LCOS is illuminated and the DMD only directs thered pixels to the screen and attempts to block unwanted red light inother places. The luminance phase pattern is created from a weighted sumof the red, green, and blue phase patterns (or other method).

FIG. 8 is a schematic illustration showing the green light path througha projector operating according to the third method where a luminancephase pattern on the LCOS is illuminated and the DMD only directs thegreen pixels to the screen and attempts to block unwanted green light inother places. The luminance phase pattern is created from a weighted sumof the red, green, and blue phase patterns (or other method).

FIG. 9 is a schematic illustration showing the blue light path through aprojector operating according to the third method where a luminancephase pattern on the LCOS is illuminated and the DMD only directs theblue pixels to the screen and attempts to block unwanted blue light inother places. The luminance phase pattern is created from a weighted sumof the red, green, and blue phase patterns (or other method).

FIGS. 10 to 13 relate to methods and apparatus which display imagesusing a plurality of light paths.

FIG. 10 illustrates a “fixed polarization” method of implementation withtwo separate laser light sources.

FIG. 11 is a schematic illustration showing a “random polarization”method of implementation and would be ideal with a fiber coupled lasersource.

FIG. 12 is a schematic illustration showing a “variable polarization”method of implementation. This is the most complicated and expensive,but allows for the most efficient use of lasers.

FIG. 13 illustrates a “fixed wavelength” method of implementation withtwo separate laser light sources.

DESCRIPTION

Throughout the following description, specific details are set forth inorder to provide a more thorough understanding of the invention.However, the invention may be practiced without these particulars. Inother instances, well known elements have not been shown or described indetail to avoid unnecessarily obscuring the invention. Accordingly, thespecification and drawings are to be regarded in an illustrative, ratherthan a restrictive sense.

This disclosure explains both a number of ways to performfield-sequential color-projection and also explains a number of ways toilluminate a DMD or other imaging element. These aspects of the presenttechnology bay be applied individually or in any combinations.

Field-Sequential Displays

Images can be formed in a projection system by using separate imageforming elements for each of red, green, and blue lights and thencombining these images on a screen. However, projector manufacturerstypically desire to make projectors as inexpensively as possible. Imageforming elements such as high quality, high resolution DMDs can beexpensive.

High dynamic range projection systems may have multiple stages ofimaging elements. These elements may cooperate to increase systemcontrast and/or reduce black level.

In some high dynamic range (“HDR”) projection systems a phase modulator(e.g. an LCOS phase modulator) may be combined with a DMD amplitudemodulator. Examples of this type of projection system are described, forexample, in WO 2015/054797, which is hereby incorporated herein byreference for all purposes. Embodiments described herein may implementany of the features described in WO 2015/054797.

To reduce the component cost, a HDR projector may use a field sequentialtechnique such that only one DMD is required. As described herein, insome embodiments, one phase modulator may be used instead of three.

DMDs typically have a fast response time. Specifically, DMDs can changethe pattern they display far faster than a human can perceive it.Instead of having a separate DMD for each colour (and thereby usingthree DMDs), one can provide a single DMD and rapidly time divisionmultiplex fields through the single DMD. Although the colours aredisplayed one-at-a time, all colours in the image are integrated by thehuman eye because the time division multiplexing occurs faster thanhumans can perceive the individual fields. This is known in the industryas “field sequential projection”.

Many phase modulators have relatively slow response times. For example,phase modulators may be LCOS based. A human observer could easilyperceive individual colour fields in a field sequential applicationwhere a single LCOS is reconfigured for the next colour between fields.

Individual LCOS panels typically cannot handle as much light as a singleDMD without damage or degradation. In systems with very high lightoutput two or more LCOS panels may be required to illuminate a singleDMD. Blue light may cause more degradation of an LCOS panel than lightof longer wavelengths (e.g. red light).

Example Field—Sequential Embodiments

Three example methods for performing field sequential projection in aprojector that uses an LCOS phase modulator and a DMD amplitudemodulator are described below. Each of these methods may be practisedusing a single DMD. The descriptions below assume a field sequentialprojector using red, green, and blue as three sequential fields.Variations of the methods described below may use different colours,more or fewer primary colours, one or more secondary colours (e.g.combinations of primary colours), and/or white as fields.

First Approach—Three Phase Modulators and One Imaging Element

A “First Approach” uses three LCOS phase modulators: one for red, onefor green, and one for blue light redirection. The first approach canprovide high light throughput and can offer high contrast and widecolour gamut.

Apparatus 10 that can operate according to the first approach isillustrated schematically in FIGS. 1 to 3. Apparatus 10 comprises aplurality of light sources 11 (11R, 11G and 11B are shown). Lightsources 11 may, for example, comprise lasers. In the illustratedembodiment, light source 11R emits red light; light source 11G emitsgreen light; and light source 11B emits blue light.

Each of light sources 11 is associated with a corresponding phasemodulator 12 (12R, 12G and 12B are shown). The phase modulators may eachcomprise an LCOS for example. Light modulated by any of phase modulators12 illuminates an imaging element 14. Imaging element 14 may, forexample, comprise a DMD. Imaging element 14 modulates the light which isthen projected onto a screen 15.

A controller 16 coordinates the operation of light sources 11, phasemodulators 12 and imaging element 14 to display an image according toimage data. One light source is active in each of a plurality ofsequential fields (each field is a period of time). In an exampleembodiment a frame rate is in the range of 20 to 100 frames per secondand each frame is divided into three fields.

In a first field as shown in FIG. 1, red light source 11R may be active.Red light from red light source 11R is steered to desired locations(e.g. locations corresponding to areas where the image data specifieshigher intensity of red) and/or steered away from undesired locations(e.g. locations corresponding to areas where the image data specifieslow intensity of red) by a phase pattern applied to phase modulator 12R.The red light modulated by phase modulator 12R is then directed ontoimaging element 14 which is controlled to modulate the incident light ina pattern specified by the image data for red light.

In second and third fields the process described above is repeated forgreen and blue light respectively as illustrated in FIGS. 2 and 3.

In this example embodiment phase modulators 12 do not need to berefreshed any faster than the frame rate (which in this example is ⅓ ofthe rate at which fields are presented). Imaging element 14 is refreshedfor every field.

For each field, controller 16 may perform steps that include:

-   -   set the imaging element to a pattern corresponding to the        corresponding color;    -   refresh a phase modulator corresponding to a different color        (the phase modulator corresponding to the current color may have        been refreshed in a previous field),    -   turn on the light source of the current color such that light        from the light source is steered by the phase modulator,        modulated by the imaging element and projected onto screen 15.

The duration of each field is short enough that the different colorsdisplayed in each field are integrated by the eyes of viewers to providethe sensation of a color image.

In example embodiments, three phase modulators (one per color) areilluminated in sequence by modulated light sources (typically lasersources). Each phase modulator is controlled to provide a phase patterncustomized for the incident beam wavelength and profile such that asteered image is generated at a steered image plane at a known distanceaway from the phase modulator. The steered images may carry higherintensity where image data specifies higher luminance for the color andlower intensity where image data specifies lower luminance for thecolor. Optical elements are provided to relay the steered images of allthree color channels along a common path to the imaging element (e.g. toa head comprising a DMD). Each steered image provides desired steeredillumination of a DMD or other imaging element. The optical elementsthat relay the steered images to the imaging element may optionallyprovide one or more of magnification, telecentricity improvement andincreasing etendue that may lead to image quality improvements andbetter compatibility with the DMD head.

The optics that guide each of the steered images to the imaging elementmay be located in the light path either after the three separate steeredimage beams have been made telecentric or before the steered imageplane. This is facilitated because the steered images are monochromatic(laser primaries) and have a high F/number (low divergence).

The phase modulators may be set to display custom patterns per colorchannel such that each steered image features a desired luminanceprofile for that color channel as well as framing (image size and shape)consistent with the steered images of the other color channels Toachieve consistent framing, the distances between each phase modulatorand its corresponding steered image plane can be selected based oncriteria such as wavelength, beam divergence and beam profile.

In embodiments that operate according to the first approach the durationthat each light source is activated (ON time for the R, G, B lightsources) may be varied based on a desired steered luminance level andcolor. For example, one can activate R, G, B sources for durations thatyield a steered full screen white with D65 white point. In cases wherethe intensity of light output by each light source can be modulated thedesired luminance and color of a displayed image may be set bycontrolling one or more of: the ON time for each light source in thecorresponding field, power output of each light source, duty cycle ofeach light source. Some benefits of modulated light sources includebeing able to use lower power lasers and drive them at the requiredhigher power with a shorter duty cycle (e.g. 30% red@2× typical maxpower).

Second Approach—One Spatially-Divided Phase Modulator and One ImagingElement

A “Second Approach” employs a single phase modulator spatially dividedinto plural areas. The phase modulator is controlled so that each areaprovides a phase pattern for one color (i.e. a phase pattern that steerslight appropriately for the corresponding color). A projector 40according to an example embodiment is illustrated in FIGS. 4, 5 and 6.

In the example embodiment light sources 11 (again 11R, 11G and 11B areprovided, for example) respectively emit red, green and blue light. Thered, green and blue light are respectively directed to illuminatecorresponding areas 43R, 43G and 43B of phase modulator 42 (which may bean LCOS for example). Areas 43R, 43G and 43B are respectively controlledto provide phase patterns for the red, green, and blue light. Thesephase patterns direct the light onto an imaging element 14. Imagingelement 14 is set in each field to modulate the light of the currentcolor. The light modulated by the imaging element 14 is projected ontoscreen 15.

The second approach may offer cost saving in comparison to the firstapproach because only a single phase modulator is required. The secondapproach may compromise contrast because light of the individual coloursmay not be steered as accurately when only a portion of a phasemodulator is used to steer the light as could be the case where anentire phase modulator is used to steer the light. The second approachalso allows for usage of the full gamut allowed by the primary colors,which may be laser primaries.

In some embodiments the physical locations on the LCOS of the areas 43corresponding to different colours can be changed from time to time forwear-leveling. The blue area 43B may age faster than the red area 43Rover time.

The division of phase modulator 42 into areas 43 need not be equal. Thesizes of some or all of areas 43 may be different. For example:

-   -   the sizes of areas 43 may be proportional to power requirements        for the different colors. Areas 43 may optionally be re-sized in        real time as power requirements for light of different colors        change.    -   area 43G may be made larger than other areas 43 due to the human        visual system's increased sensitivity to the accuracy of green        light; or    -   area 43B for blue may be increased to provide lower power        density and reduced aging.

In the second approach, each area 43 of phase modulator 42 needs to berefreshed at most once per frame. All areas 43 of phase modulator 42 maybe refreshed in one operation. In cases were the different areas 43 ofphase modulator 42 can be individually refreshed one area 43 may berefreshed while light is being steered by another area 43.

When a single phase modulator is spatially divided, a geographic portionof the LCOS is used for each individual colour. Each portion is drivenwith a corresponding phase image. All three phase images are computed,scaled, and combined into a single phase image that is applied to theLCOS phase modulator.

Each light source 11 (e.g. each laser) is directed to illuminateexclusively the corresponding colour region on the LCOS modulator 42. Nopart of the LCOS should be illuminated by more than one laser colour.

For wear leveling, lasers may be from time to time redirected todifferent regions of the LCOS to change where blue is. Blue light agesLCOS devices faster than red or green light.

In example embodiments that implement the second approach a single phasemodulator is illuminated in sequence by each of a plurality of modulatedlight sources but each light source only illuminates a correspondingportion of that single phase modulator. The size of the portion of phasemodulator allocated for each color may be determined by desired steeredimage quality (in general, everything else being equal the more pixelsallocated for a color the better the quality of the steered image willbe for that color). Each color-specific portion of the phase device maybe controlled to provide a phase pattern customized for the wavelengthof light of the color, incident beam profile/quality, etc. such that thesteered image formed by that portion will overlap with the steeredimages of the other channels (i.e. framing should be consistent).

In some embodiments to form RGB steered images at a steered image planea common distance from the phase modulator the phase patterns of eachcolor portion may be computed using target images with differentgeometries (i.e. the target images for different colors may be scaleddifferently to compensate for wavelength effects on steering). As insome embodiments which apply the first approach optical elements thatrelay the steered images to the imaging element may optionally provideone or more of magnification, telecentricity improvement and increasingetendue that may lead to image quality improvements and bettercompatibility with the DMD head.

Color combination optics are optionally present but are typically notnecessary following the phase modulator since the steered images foreach color may be provided at a common steered image plane in afield-sequential manner. Color combination optics may be provided toaggregate the incident light from the 3 portions of the phase modulatorsuch that the paths taken by the R, G, B beams as they are incident onthe imaging element are closely spaced and parallel or nearly parallel.If the incident beams are not perfectly-parallel the correspondingcolor-specific phase patterns may provide tilt correction.

Third Approach—One Common Phase Modulator and One Imaging Element

A “Third Approach” employs a single LCOS phase modulator displaying asingle phase pattern for each frame. This is the most cost effectivemethod due to the fact that it uses a single phase modulator and onlyone phase pattern needs to be computed (instead of 3) such that lessexpensive computational hardware may be used. The third approach maycompromise colour gamut because it can allow more leakage of unwantedcolours through the system (due to not steering unwanted colourcomponents). The third approach can provide contrast almost on par withthe first approach.

FIGS. 7, 8, and 9 schematically illustrate apparatus 70 configured foroperation according to the third approach. Apparatus 70 includes lightsources 11 (again 11R, 11G and 11B are provided, for example) thatrespectively emit red, green, and blue light. The red, green, and bluelight is respectively directed to illuminate phase modulator 72 (whichmay comprise an LCOS for example). Phase modulator 72 is set with aphase pattern that is selected to steer light from any one of lightsources 11 onto an imaging element 14. The same phase pattern may beused for two or more different colors of light.

Imaging element 14 is set in each field to modulate the light of thecurrent color. The light modulated by the imaging element 14 isprojected onto screen 15.

Phase modulator 72 may be updated with a new pattern once per frame ormore seldom than that if the intensity distribution for successiveframes is the same or similar.

Luminance Phase Modulation Images

If a single phase image is used to direct light for all colours (as forexample when applying the third approach discussed above), it shoulddirect sufficient light to the DMD in any area where any colour ispresent to illuminate all the image features.

The DMD is controlled to block any unwanted colours from the screen foreach image feature. The ability of the DMD to block light determines thesize of the final gamut (because a pure red object will have a smallamount of green and blue light leaked on it).

One way to create a luminance image from an RGB image (i.e. image datathat specifies R, G and B values for individual pixels) is to convert anRGB image to the XYZ colour space and to use the Y channel as theluminance image.

In certain embodiments that implement the third approach, a single phasemodulator is illuminated in sequence by modulated light sources ofdifferent colors. Each light source may illuminate substantially all ofan active area of the phase modulator. A common phase pattern is used tosteer light for all three color channels such that the steered imageshave the desired luminance profile and the combination of the steeredimages provides the same color point.

Since the phase pattern is common for all colors one may direct beamsfrom the different-colored light sources to be incident on the phasemodulator at different angles such that three steered images areproduced at different distances and along different orientationsrelative to the phase modulator. Separate color combination and relayoptics may then be used to recombine, shape and relay the separatesteered images onto the imaging element. This construction can be usedto match the framing of the different colors.

Another way to match the framing of different color channels is to makebeams of different colored light incident on the phase modulator in aparallel fashion but to modify the collimation of some or all of thebeams so some or all of the beams are slightly diverging or converging.The amount of divergence or convergence of each beam may be selected tocompensate for the different distances at which steered images wouldotherwise be formed for the different colors. The steered images canthen be relayed onto the imaging element. As in the other approaches,projectors that apply the third approach may optionally include opticalelements that magnify, improve telecentricity and/or increase etendue.

Approaches for Illuminating an Imaging Element

Another aspect of this invention provides methods and apparatus to moredirectly illuminate a DMD and/or to selectively illuminate a DMD orother amplitude modulator with light that is somehow pre-modulatedand/or with light that is more directly delivered from a light source tothe amplitude modulator. Such methods and apparatus may direct a portionof light from a source to a DMD bypassing a phase modulator or otherup-stream light-attenuating component and/or may add one or more secondlight sources directed to illuminate the DMD only. Direct illuminationof the DMD may help to boost efficiency when displaying bright scenes.

Methods and apparatus of this aspect may be applied individually or maybe combined with methods and apparatus according to any of the firstapproach to the third approach, which are discussed above. Such methodsand apparatus may also be applied in colour projection systems whichinclude three complete sets of LCOS and DMD.

In high dynamic range projection systems an LCOS phase modulator may becombined with an amplitude modulator (e.g. a DMD) such that the LCOSphase modulator steers to locations on the amplitude modulator where itis needed.

In the case of full screen white or very bright images, it is moreefficient to illuminate a DMD directly as opposed to using the phasemodulator to steer light onto the DMD. LCOS panels typically cannothandle as much light energy as a DMD so total system light throughputcapacity may be increased by allowing at least some light to bypass theLCOS modulator at least when a bright image is being projected.

Some embodiments combine light being steered by a phase modulator withlight bypassing the phase modulator such that the combined light arrivesat the DMD at a uniform angle of incidence. This addresses the problemthat DMDs are often very sensitive to the angle that light approaches.Light that bypasses the LCOS and light that was steered by the LCOS maybe combined such that it all is incident on the DMD at the same angle(i.e. within a small range of angles of incidence that the DMD canaccommodate). In some embodiments, this is achieved using a combinerthat combines light incident on the combiner from two differentdirections into a combined beam of light that leaves the combiner in acommon direction. The combiner may comprise, for example, a polarizingbeam splitter or dichroic element.

FIGS. 10 through 13 illustrate example apparatus which can be operatedto illuminate an imaging element such as a DMD with:

-   -   light that has been steered by a phase modulator (and/or        processed by some other upstream light attenuating optical        element);    -   light that has been directed to illuminate the imaging element        without being steered by the phase modulator; or    -   blends of the above.        The light that has been steered by the phase modulator and the        light that has not been steered by the phase modulator may come        from the same or different light sources.

Light may be selectively caused to propagate on different paths usingpolarization. For example, light can be P polarized, S polarized, orboth (random polarization). S and P polarized lights are polarized atright angles to each other. Light of S and P polarizations can beseparated from one another with a polarizing beam splitter. P and Spolarized light can be combined to random, and random can be split intoP and S using a polarized beam splitter.

Laser light sources with random polarization have large components ofboth S and P polarizations. Free space lasers tend only to produce S orP polarized light depending on the physical orientation of the laser.Physically rotating the laser can change whether the emitted light is Sor P polarized.

LCOS phase modulators tend to function well only with a single type ofpolarization (depending on orientation). For instance if a LCOS panel isoriented for P-polarized light, it will tend to reflect S-polarizedlight directly back toward the source instead of allowing theS-polarized light to pass.

Using a LCOS modulator to steer light from a P polarized source allowsfor combination of steered P-polarized light with non-steered Spolarized light before directing the resulting combined random polarizedlight to the DMD amplitude modulator.

Fixed Polarization Approach

In some embodiments, two separate light sources, e.g. banks of lasers,can be used; one to produce S polarized light and one to produce Ppolarized light (the “fixed polarization” approach). Light from one ofthe light sources (e.g. the P-polarized light) is directed to illuminatean imaging element (e.g. a DMD) by way of a steering element (e.g. anLCOS). Light from other light source(s) (e.g. the S-polarized sources)is directed to illuminate the imaging element without interacting with(i.e. bypassing) the steering element. If the bypass light (e.g. theS-polarized light) is not desired at the imaging element, for examplebecause the scene displayed is very dark, the source of bypass light(e.g. the S-polarized light source) can be turned down or off and/ordirected away from and/or blocked from reaching the imaging element.

FIG. 10 illustrates a projector 100 which implements a “fixedpolarization” approach with two separate laser light sources 11S and11P. Light source 11P illuminates a phase modulator 12 with P-polarizedlight. Phase modulator 12 is set with a phase pattern that steers theP-polarized light onto an imaging element 14 such as a DMD by way of acombiner 108 which, in this embodiment, comprises a polarizing beamsplitter.

Light source 11S emits S-polarized light that is homogenized by passingthrough an optical system 109 and directed onto combiner 108. Opticalsystem 109 makes the light that passes through it be uniformlydistributed (or distributed in another desired way at the imagingelement). Optical system 109 may, for example, comprise a fly-eye arrayand/or other homogenizer.

Any light from light source 11S is combined at combiner 108 with lightfrom light source 11P and directed to illuminate imaging element 14.

A despeckling element 107 is optionally provided in the light pathupstream from imaging element 14. The despeckling element despeckles thecombined beam. The optional despeckling element may be providedimmediately before the DMD amplitude modulator, for example.

DMDs and other amplitude modulators are not perfect at blocking light,so in scenes with a lot of dark it is desirable to stop light that doesnot originate from the phase modulator from hitting the DMD.

A control system 101 may be connected to control light sources 11P and11S. In some embodiments light sources 11P and 11S have outputs that areindividually controllable. In some embodiments control system 101 maycontrol the output of light from light source 11S. In some embodimentscontrol system 101 may switch light source 11S on or off depending uponwhether additional light is required. Control system 101 may alsocontrol the application of data to phase modulator 12 and imagingelement 14 and the overall timing of operation of apparatus 100.

Random Polarization (or Unpolarized) Approach

A single source of light may be used (likely fiber-coupled LEDs) thatemits both S and P polarization (the “random polarization” approach). Inthis case, a polarizing beam splitter can be employed to separate the Sand P components of the incoming light into two separate paths. Anattenuator such as an aperture, and/or a shutter and/or a controllableredirection element such as a movable mirror or lens may be provided inthe S (bypass) light path to attenuate the light bypassing the phasemodulator in cases where dark blacks are required. The P component maybe modulated (e.g. steered by a phase modulator) before it is incidenton the amplitude modulator.

FIG. 11 is a schematic illustration of an example apparatus 110configured to operate according to the random polarization approach.Apparatus 110 comprises a light source 11SP that emits light thatincludes plural separable polarization components (e.g. S- andP-polarized components). Light source 11SP may beneficially butoptionally comprise a fiber coupled laser source.

It is preferable that light emitted by light source 11SP has good beamquality (i.e. low etendue) which allows it to be collimated with a smalldivergence. This then allows for better separation (e.g. betteruniformity and higher throughput) of the S and P-polarized components atbeam splitter 112 into paths 111A and 111B.

Homogenizer 115 is preferably chosen such that the etendue of the lightalong path 111B does not increase significantly. This facilitatescombining the beams of light at combiner 114. One suitable choice forhomogenizer 115 is a lens combination that includes a fly's eye lensarray where such a combination can provide homogenization with minimalincrease in etendue.

Embodiments as illustrated in any of FIGS. 10 to 13 can benefit fromusing low etendue light. The low etendue facilitates efficiency,uniformity, etc. when different beams of light are combined.

Light emitted by light source 11SP is divided based on polarization intotwo paths 111A and 111B by a beam splitter 112. Path 111A carries lightto illuminate an imaging element 14 by way of a phase modulator 12. Path111B bypasses phase modulator 12. Paths 111A and 111B merge at acombiner 114 upstream from imaging element 14.

Path 111B includes a homogenizer 115 and an aperture 116. Aperture 116may be controlled to adjust the amount of light incident on imagingelement 14 that is delivered by bypass path 111B.

A control system 115 may control aperture 116 to selectively regulatethe amount of light from path 111B that is allowed to reach imagingelement 14. Control system 115 may also control the application of datato phase modulator 12 and imaging element 14 and the overall timing ofoperation of apparatus 110.

Variable Polarization Approach

A “variable polarization” approach is similar to the random polarizationapproach but provides a way to vary the relative intensities of theseparable polarization components of the light emitted by the lightsource. For example, apparatus that implements the variable polarizationapproach may comprise a half wave plate that can be quickly rotatedwithin 90 degrees. By setting rotation of the half wave plate on aframe-by-frame basis, one can adjust the mixture of S and Ppolarizations sent to the polarization beam splitter. The resulting beammay be used as the input to the “random polarization” apparatusdescribed above and allow for more light to be sent directly to the DMD(e.g. more S-polarized light) for bright scenes and more to the LCOS(e.g. more P-polarized light) for dark scenes.

FIG. 12 is a schematic illustration showing apparatus 120 thatimplements the “variable polarization” approach. The FIG. 12 embodimentis typically more complicated and expensive to make than the embodimentsof FIGS. 10 and 11 but allows for the most efficient use of lasers.

The portion of apparatus 120 shown inside box 121 is common to apparatus110 which is described above. Apparatus 120 comprises a light source 11that emits polarized light. The polarization of the light can be alteredby a polarization shifting element 122. The polarization shiftingelement may be controlled to alter the relative amounts of twopolarization states in the light that are separable by beam splitter112. For example, polarization shifting element 122 may comprise ahalf-wave plate and a motor or other actuator connected to set an angleof rotation of the half-wave plate.

A control system 125 may control polarization shifting element 122 toselectively regulate the amount of light that enters path 111B. Controlsystem 125 may also control the application of data to phase modulator12 and imaging element 14 and the overall timing of operation ofapparatus 120.

Wavelength-Based Separation Approaches

Other approaches to control paths taken by light separate light based onwavelength. Different wavelengths of light can be separated with adichroic element or multilayer thin film, for example. Thus a system canbe created that has 2 sets of reds, greens, and blues. The reds, greens,and blues may be selected such that a large gamut can be created witheither set and the absence of one is not noticeable.

In a similar manner to the above, two light sources, e.g. two lasers,with similar wavelengths can be used where one wavelength is sent to theLCOS or other phase modulator and the other wavelength is provideddirectly (e.g. without significant attenuation) to the DMD or otheramplitude modulator using a colour beam splitter (the “fixed wavelength”approach). The two wavelengths may correspond to the same primary colour(e.g. the two wavelengths may be different reds, greens, or blues).

FIG. 13 illustrates schematically apparatus 130 that implements a “fixedwavelength” approach with two separate laser light sources 11R1 and 11R2that emit light of different wavelengths. The wavelengths may be closelyspaced, for example, separated by differences of 5 nm or 10 nm. In otherembodiments the two wavelengths may be more widely separated. Thewavelengths could be two shades of the same color, for example twoshades/tones of red, green or blue.

Light source 11R1 illuminates an imaging element 14 by way of a phasemodulator 12. Light source 11R2 illuminates imaging element 14 by way ofa light path that bypasses phase modulator 12. Light from light sources11R1 and 11R2 are combined at a combiner 132. Optics 139 homogenizelight in light path 11R2.

A control system 135 may be connected to control light sources 11R1 and11R2. In some embodiments light sources 11R1 and 11R2 have outputs thatare individually controllable. In some embodiments control system 135may control the output of light from light source 11R2. In someembodiments control system 135 may switch light source 11R2 on or offdepending upon whether additional light is required. Control system 135may also control the application of data to phase modulator 12 andimaging element 14 and the overall timing of operation of apparatus 130.

DC Spot Recycling

Phase modulators can produce a DC spot that does not correspond to animage feature. It is normally desirable to steer the DC spot out of theimage. The light from this spot may be recovered and sent to the DMD orother imaging device, for example, as diffuse light. Whether or notlight from the DC spot is directed to the imaging device and/or anamount of light from the DC spot to be directed to the imaging device iscontrolled on a frame-by frame or a field-by-field basis in someembodiments. The control may be based on a power level calculated for afield or frame. For higher power levels (brighter images) light from theDC spot may be directed to the imaging device whereas for lower powerlevels less or no light from the DC spot may be directed to the imagingdevice. A wide range of optical systems may be used to carry light fromthe DC spot to the imaging device. In some embodiments an arrangementsimilar to that shown in FIG. 10 may be used to collect light from theDC spot and combine that light with light that has been modulated by thephase modulator upstream from the imaging device. The optical path forlight from the DC spot may include optical elements such as one or morehomogenizers or light diffusers to make the added illumination providedby light from the DC spot diffuse at the imaging device. If necessary apolarization shifting element may be provided to alter the polarizationof light from the DC spot to facilitate combination of light from the DCspot with light that has been steered by the phase modulator. Thistechnique may be combined with any of the above or used on its own.

The various approaches described herein may be embodied in projectorsconfigured to implement these approaches. Further, any of the describedmethods for field-sequential imaging may optionally be combined with anyof the described methods for providing direct illumination of a lightmodulator. An LCOS is an example of a phase modulator. Other embodimentsmay use other types of phase modulator. A DMD is an example of anamplitude modulator. Other embodiments may use amplitude modulators ofother types in place of a DMD.

In an example embodiment, video image data is processed to identify adegree of brightness of a frame. If the frame is dark then a phasemodulator may be controlled to steer light from a light source onto anamplitude modulator and to control the amplitude modulator to modulatethe steered light to display the image specified for the frame. In aframe sequential image this may be done separately for each coloursub-frame. If the frame is bright then the amplitude modulator may beilluminated by light that is not first steered by the phase modulator,either in addition to or instead of light steered by the phasemodulator. The amplitude modulator may be controlled to display the(bright) image.

In some example embodiments apparatus as illustrated in any one of FIGS.11, 12, 13 may be used to provide one of a plurality (e.g. 3 to 6 insome embodiments) of color channels. In some embodiments two or more ofor all of the color channels modulate light of the respective color inparallel (i.e. at the same time). In other embodiments some or all ofthe color channels may operate in a field-sequential manner or atime-interleaved manner. In some cases field-sequential operation isachieved using one of approaches one, two or three which are discussedabove for some or all of the color channels.

In some embodiments a plurality of colors from separate color channelswhich have the general architecture illustrated by FIG. 11, 12 or 13 areemitted simultaneously and combined to provide white light.

Displays as described herein may include other elements not shown forclarity such as: controllers which are configured to control one or morephase modulators and one or more amplitude modulators to display imagesor other light patterns; inputs or data stores by way of which imagedata is supplied; light sources (which may comprise lasers, othersolid-state light sources, or other light sources entirely); projectionlenses; display screens (front or rear projection); other opticalelements in light paths (e.g. lenses, mirrors, collimators, diffusers,etc.); power supplies; focusing systems; heat management systems, etc.

Interpretation of Terms

Unless the context clearly requires otherwise, throughout thedescription and the claims:

-   -   “comprise”, “comprising”, and the like are to be construed in an        inclusive sense, as opposed to an exclusive or exhaustive sense;        that is to say, in the sense of “including, but not limited to”;    -   “connected”, “coupled”, or any variant thereof, means any        connection or coupling, either direct or indirect, between two        or more elements; the coupling or connection between the        elements can be physical, logical, or a combination thereof;    -   “herein”, “above”, “below”, and words of similar import, when        used to describe this specification, shall refer to this        specification as a whole, and not to any particular portions of        this specification;    -   “or”, in reference to a list of two or more items, covers all of        the following interpretations of the word: any of the items in        the list, all of the items in the list, and any combination of        the items in the list;    -   the singular forms “a”, “an”, and “the” also include the meaning        of any appropriate plural forms.

Words that indicate directions such as “vertical”, “transverse”,“horizontal”, “upward”, “downward”, “forward”, “backward”, “inward”,“outward”, “left”, “right”, “front”, “back”, “top”, “bottom”, “below”,“above”, “under”, and the like, used in this description and anyaccompanying claims (where present), depend on the specific orientationof the apparatus described and illustrated. The subject matter describedherein may assume various alternative orientations. Accordingly, thesedirectional terms are not strictly defined and should not be interpretednarrowly.

Embodiments of the invention may be implemented using control systemsthat include specifically designed hardware, configurable hardware,programmable data processors configured by the provision of software(which may optionally comprise “firmware”) capable of executing on thedata processors, special purpose computers or data processors that arespecifically programmed, configured, or constructed to perform one ormore steps in a method as explained in detail herein and/or combinationsof two or more of these. Examples of specifically designed hardware are:logic circuits, application-specific integrated circuits (“ASICs”),large scale integrated circuits (“LSIs”), very large scale integratedcircuits (“VLSIs”), and the like. Examples of configurable hardware are:one or more programmable logic devices such as programmable array logic(“PALs”), programmable logic arrays (“PLAs”), and field programmablegate arrays (“FPGAs”). Examples of programmable data processors are:microprocessors, digital signal processors (“DSPs”), embeddedprocessors, graphics processors, math co-processors, general purposecomputers, server computers, cloud computers, mainframe computers,computer workstations, and the like. For example, one or more dataprocessors in a control circuit for a device may implement methods asdescribed herein by executing software instructions in a program memoryaccessible to the processors.

Processing may be centralized or distributed. Where processing isdistributed, information including software and/or data may be keptcentrally or distributed. Such information may be exchanged betweendifferent functional units by way of a communications network, such as aLocal Area Network (LAN), Wide Area Network (WAN), or the Internet,wired or wireless data links, electromagnetic signals, or other datacommunication channel.

For example, while processes or blocks are presented in a given order,alternative examples may perform routines having steps, or employsystems having blocks, in a different order, and some processes orblocks may be deleted, moved, added, subdivided, combined, and/ormodified to provide alternative or subcombinations. Each of theseprocesses or blocks may be implemented in a variety of different ways.Also, while processes or blocks are at times shown as being performed inseries, these processes or blocks may instead be performed in parallel,or may be performed at different times.

In addition, while elements are at times shown as being performedsequentially, they may instead be performed simultaneously or indifferent sequences. It is therefore intended that the following claimsare interpreted to include all such variations as are within theirintended scope.

Software and other modules may reside on servers, workstations, personalcomputers, tablet computers, image data encoders, image data decoders,PDAs, video projectors, audio-visual receivers, displays (such astelevisions), digital cinema projectors, media players, and otherdevices suitable for the purposes described herein. Those skilled in therelevant art will appreciate that aspects of the system can be practisedwith other communications, data processing, or computer systemconfigurations, including consumer electronics (e.g., video projectors,audio-visual receivers, displays, such as televisions, and the like),set-top boxes, network PCs, mini-computers, mainframe computers, and thelike.

The invention may also be provided in the form of a program product. Theprogram product may comprise any non-transitory medium which carries aset of computer-readable instructions which, when executed by a dataprocessor, cause the data processor to execute a method of theinvention. Program products according to the invention may be in any ofa wide variety of forms. The program product may comprise, for example,non-transitory media such as magnetic data storage media includingfloppy diskettes, hard disk drives, optical data storage media includingCD ROMs, DVDs, electronic data storage media including ROMs, flash RAM,EPROMs, hardwired or preprogrammed chips (e.g., EEPROM semiconductorchips), nanotechnology memory, or the like. The computer-readablesignals on the program product may optionally be compressed orencrypted.

In some embodiments, the invention may be implemented in software. Forgreater clarity, “software” includes any instructions executed on aprocessor, and may include (but is not limited to) firmware, residentsoftware, microcode, and the like. Both processing hardware and softwaremay be centralized or distributed (or a combination thereof), in wholeor in part, as known to those skilled in the art. For example, softwareand other modules may be accessible via local memory, via a network, viaa browser or other application in a distributed computing context, orvia other means suitable for the purposes described above. In someembodiments image data is processed by a processor executing softwareinstructions to yield control signals for a phase modulator. Thesoftware may execute in real time in some embodiments (other embodimentsare also possible).

Where a component (e.g. a software module, processor, assembly, device,circuit, etc.) is referred to above, unless otherwise indicated,reference to that component (including a reference to a “means”) shouldbe interpreted as including as equivalents of that component anycomponent which performs the function of the described component (i.e.,that is functionally equivalent), including components which are notstructurally equivalent to the disclosed structure which performs thefunction in the illustrated exemplary embodiments of the invention.

Specific examples of systems, methods and apparatus have been describedherein for purposes of illustration. These are only examples. Thetechnology provided herein can be applied to systems other than theexample systems described above. Many alterations, modifications,additions, omissions, and permutations are possible within the practiceof this invention. This invention includes variations on describedembodiments that would be apparent to the skilled addressee, includingvariations obtained by: replacing features, elements and/or acts withequivalent features, elements and/or acts; mixing and matching offeatures, elements and/or acts from different embodiments; combiningfeatures, elements and/or acts from embodiments as described herein withfeatures, elements and/or acts of other technology; and/or omittingcombining features, elements and/or acts from described embodiments.

It is therefore intended that the following appended claims and claimshereafter introduced are interpreted to include all such modifications,permutations, additions, omissions, and sub-combinations as mayreasonably be inferred. The scope of the claims should not be limited bythe preferred embodiments set forth in the examples, but should be giventhe broadest interpretation consistent with the description as a whole.

What is claimed is:
 1. An image projector comprising: a first bank oflasers operable to emit light having a first polarization state; asecond bank of lasers operable to emit light having a secondpolarization state different from the first polarization state; anoptical combiner arranged to combine the light from the first and secondbanks of lasers and to direct the combined light onto an imaging elementoperative to spatially modulate the combined light; a phase modulatorlocated in a light path between the first bank of lasers and the opticalcombiner, the phase modulator operable to display a phase pattern whichcauses the light having the first polarization state to be selectivelysteered to desired locations on the imaging element; and a projectionlens operative to project the combined light that has been modulated bythe imaging element.
 2. The image projector according to claim 1 whereinthe first polarization state is a P-polarized state and the secondpolarization state is an S-polarized state.
 3. The image projectoraccording to claim 1 wherein the light from the first and second banksof lasers is incident on the imaging element with the same angle ofincidence.
 4. The image projector according to claim 1 comprising anoptical homogenizer in a light path between the second bank of lasersand the imaging element.
 5. The image projector according to claim 4comprising an aperture between the optical homogenizer and the imagingelement, the aperture controllable to adjust the amount of light fromthe second bank of lasers that is incident on the imaging element. 6.The image projector according to claim 1 wherein the imaging elementcomprises an amplitude modulator.
 7. The image projector according toclaim 6 wherein the amplitude modulator comprises a DMD.
 8. The imageprojector according to claim 1 wherein the phase modulator comprises anLCOS phase modulator.
 9. The image projector according to claim 1wherein the optical combiner comprises a color beam splitter.
 10. Theimage projector according to claim 1 wherein the optical combinercomprises a dichroic mirror.
 11. The image projector according to claim1 comprising a controller operative to control an output of the firstand second banks of lasers in response to image data.
 12. The imageprojector according to claim 1 comprising a controller configured toprocess video image data to identify a degree of brightness of a frameand, if the frame is dark to control the phase modulator to steer lightfrom the first bank of lasers onto the imaging element and to controlthe imaging element to modulate the steered light to display an imagespecified for the frame.
 13. The image projector according to claim 12wherein the controller is further configured to, if the frame is bright,cause the imaging element to be illuminated by light from the secondbank of lasers that has not been steered by the phase modulator.
 14. Theimage projector according to claim 1 wherein the imaging elementcomprises an amplitude modulator configured to restore finer details ofa target image.
 15. The image projector according to claim 1 wherein theimaging element is part of a refinement module and the refinement modulecomprises a de-speckling module.
 16. The image projector according toclaim 1 wherein the imaging element is part of a refinement module andthe refinement module comprises a polarization-varying device.
 17. Theimage projector according to claim 1 wherein the imaging element is partof a refinement module and the refinement module is operative to providehigh spatial frequency detail to a light-field provided by the combinedlight that has been modulated by the imaging element.
 18. The imageprojector according to claim 17 wherein the refinement module isoperative to minimize visual artifacts introduced by the phase modulatorinto the combined light.
 19. The image projector according to claim 1comprising a unit configured to analyse the light from the first path.20. The image projector according to claim 1 comprising a controllerconfigured to process video image data to identify a degree ofbrightness of a frame and based on the degree of brightness switch thesecond bank of lasers on or off.